Microphone.



H. E. SHREEVE. MICROPHONE. APPLICATION FILED SEPT. 2, 1909.

1,026,057. Patented May14,1912.

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HERBERT IE. SHBEEVE,- OF WYOMING, NEW JERSEY; ASSIGNOR T WESTERN ELEG- TIRIG COMPANY, 01? NEW YORK, N. 33., A CORCEQRIATION OF ILLINOIS.

MICROPJEIONE.

Specification of Letters Patent.

Patented May Ht, 1912.

Application filed September 2, 1909. Serial No. 515,837.

The object is to provide an instrument of this character which will be simple, compact, cheap to manufacture and efficient in use, having comparatively "few parts, which are assembled in such manner as to be readily accessible for purposes of repair, adjustment or substitution of parts.

The invention consists in certain details of construction and combinationsof parts,'

as will be hereinafter set forth by reference to the accompanying drawings, Wherein- Figure 1 1s a vertical sectional View of the instrument with the parts assembled; Fig. 2 is a rear View of the cap with. the bridge secured in place; Fig. 3 is a front. view of the back plate showing the terminal connections; Fig. 4 is a front view of the bridge; Fig. 5 shows the various ele- "ments which go to make up the transmitter, (excepting the granular carbon) showing said ports in the relative positions they assome when assembled.

A concave circular cap or face plate 1, perforated at its center, is provided upon its interior with threads 2, with which threads a casing or back plate 3, exteriorly to threaded, is adapted to engage. Upon the interior face of said cap, a peripheral raised portion 4, fori'ning a rim, is provided, upon which adapted. to rest a mica diaphragm 5. Lying: flush with said mica diaphragm is the front electrode, which in the present instance is a thin carbon diaphragm G. The

bridge 7 is provided vith a depressed por tion 8 for engagement with said carbon diaphragm 6, and upon this depressed portion an annulus 9, threaded upon its exterior, as at 10, is :ulapted to engage with tlie'threaded portion 2 of said cap and "clamp said bridge 7 carbon diaphragm 6 and mica. diaphragm o to said rim or raised portion d of the cap. The ring 9 has holes 11, 1:2, diametrically opposite each other, with which a special tool is adapted to engage in screwing dhwn said ring and thereby clamping said parts to the cap 1. The center of said bridge 7 is provided with a recess 13, preferably annular. at the bottom of which ,is ."ecurcll upon an insulating Washer 14 the rear clcctri'ide, in the form 01 a circular carbon block, 15, the construction and arrangement being such that the face of said block projects slightly above the surrounding surface of said bridge and is: clear and free from the sides oi. said recess. Ranged around the center of said carbon block 15 is a. series of hemispherical cavilies 16, havinghighly polished faces and being partially filled with a conducting medium 17, in the present instance, granular carbon. The relative position oi said carbon block 15 with respect to said diaphragp 6 is such that while the said block does not actually contact with said diaphragm, yet they are so intimate that the carbon granules contained in said cavities will not escape, but are held therein by said diaphragm. A bolt 18, passing through an opening 15) in the center of said carbon block 15 and through the insulating washcrs ll and on either side of the base of said annular recess, is secured in the bottom of said re s by a nut 21 on the under side of the base of said recess. The head of said boll 18,1ics slightly below the face of said carbon "block.

Bearing against and making electrical connection with a platinum point 23 secured to the projecting end of said bolt is a platinum tipped spring 22, anchored at its opposite end to a terminal bloclt'Qd. Secured upon the casing 3 is a post it) to which a conductor leading from the other circuit terminal of the instrument may be attached. The connecting lug 25 may lso, if desired, be mounted on the terminal block 24:. A locking ring 26 is provided on the easing with which the cap 1 is :ulaptcd'to engage at the limit of its movement.

Having thus described my invention, 1 claim:

l. in a microphone, the combination with a mouthpiece, of a movable electrode and a hridg'e clamped against the inner face of said mouthplecc by an adpistable annulus,

a plurality of openings in said bridge, a lined electrode secured in a. recess in said bridge with its face in intimate relation to, but not actually touching, said movable electrode, a depression in said fixed electrode, granular material partially' filling said depression and held therein by contact with said movable electrode a back plate or casing adapted to beremovably secured to said mouthpiece, and a locking ring for said arts.

2. a microphone, the combination with a cap formin the mouthpiece, said cap being interior y threaded and having a raised rim near the periphery of its interiorface, a mica diaphragm resting upon said rim, ,a thin carbon diaphragm adapted to lie flush with said mica iaphragm, a metal- I lie bridge provided with a series of openings, the periphery of said bridge restin upon said carbon diaphragm, a threade rm adapted to clamp said diaphragms and bri ge to said cap, an annular recess in the center of said bridge, a carbon block secured in said recess with its face in intimate juxtaposition to said carbon diaphragm, a lurality of hemispherical cavities in the ace of said block, the surfaces of said cavities being highly polished, each of said cavities containing carbon granules held therein by contact with said diaphragm, a back plate or casing adapted for screw threaded engagement with said face late, a terminal block in said back plate an having mounted thereon the leading-in wires, and a locking ring for maintaining permanent the adjustment of said front and back plate.

In witness whereof, I hereunto subscribe my name this 31st day of August A. D., 1909.

HERBERT E. SHREEVE.

\Vitnesses:

IRVING MACDONALD, EDGAR F. BEAUBIEN. 

